The electronic throttle valve receives an input signal from the PCM. Depending on the operating state of the engine, a change in the position of the throttle plate may not be necessary when the acellerator pedal position (APP) sensor position changes. An electric motor moves the throttle valve shaft by means of a set of gears. The throttle valve position is continuously measured by the TP sensors, and the information about the position is processed and monitored by the PCM. If one of the two TP sensors is faulty, the signal from the intake sensor is used. However, the torque is limited by the PCM. The system switches into an emergency running mode in the event of a defect on both TP sensors, on the throttle valve motor, or if the intact sensor cannot be detected. In this emergency running mode the current supply to the electric throttle valve motor is interrupted. Instead, the throttle valve is closed by means of a spring against a spring-loaded end stop. With the throttle valve position kept constant, the ignition angle and the injected fuel quantity are then varied to meet the torque demands. The stop screw incorporates a spring-loaded pin which enables the throttle valve to be closed beyond the emergency running position (e.g. for idle control or deceleration fuel shut-off). If the difference between the TP sensor values is very great, the larger of the two values is taken to bring the emergency running mode into play. Here again the maximum torque is limited by the PCM. Whenever emergency running mode is selected a diagnostic trouble code (DTC) is stored in the PCM. These codes can be read out with WDS.
Mass air flow (MAF) sensor
